The present invention relates, in general, to novel thermally protected and corrosion protected structures. More particularly, the present invention relates to such structures that comprise in combination a core substrate and a concentric laminate, especially where the core substrate comprises a metallic tendon, and even more especially a tendon used in an external post-tensioning system.
Structural systems and methods can utilize internal or external post-tensioning tendons which are typically metallic and can comprise strands, wires and/or bars. Tendons can consist of either single or multiple metallic elements and can be used, for example, in concrete construction, steel construction, and timber construction as well known to those of skill in the art. External tendons do not have the benefit of being surrounded by concrete or other protection, and therefore are much more susceptible to corrosion and damage from heat in the event of a fire.
In the past, it has been common for an external tendon to be protected by providing duct to surround the tendon, and then injecting suitable grout into the duct. This method functions well to protect an external tendon, but this method also is quite an expensive process.
It is thus quite desirable to provide an efficient and cost-effective structure and method by which to protect such external tendons. It is also desirable to provide an efficient and cost-effective structure and method for protecting from corrosion and heat any core substrate such as, for example, metallic data lines, electrical power lines or other suitable materials.
Of interest to the present invention, U.S. Pat. No. 6,074,714 to Gottfried discloses a fire and heat protection wrap that includes a concentric composite laminate structure having a plurality of concentric layers for the protection of structural steel components (columns, beams and open web joints), which are exposed to high temperatures of up to 5 hours in duration. The plurality of concentric layers includes an outer first layer, an inner second layer, an inner third layer, and an inner core fourth layer. The outer first layer is a fiberglass textile having an intumescent coating resistant to heat, water, and impact. Each of the inner second layer and the inner core fourth layer is a metal foil layer for reflecting heat and eliminating the convection transfer of heat. The inner core third layer is a low conductivity refractory blanket for reducing the transmission of heat.
Also of interest, U.S. Pat. No. 5,985,385 to Gottfried discloses a fire and heat protection wrap for conduits, cable trays, other electrical transmission lines, and gas and oil pipelines. The protection wrapping system includes a concentric composite laminate structure having a plurality of concentric layers for the protection of electrical transmission lines, gas pipelines, and oil pipelines that are exposed to high temperatures in excess of 3 hours in duration. The plurality of concentric layers includes an outer first layer, an inner second layer, an inner third layer, and an inner core fourth layer. The thermal protection wrapping system is effective at continuously maintained temperatures up to 2200xc2x0 F. (1215xc2x0 C.) for at least 3 hours in duration.
Additionally of interest, U.S. Pat. No. 5,603,990 (continuation-in-part) and U.S. Pat. No. 5,487,946 (parent), both to McGinniss et al., disclose an intumescent coating system and method for thermally protecting a substrate having a surface exposed to a flame environment. The coating system has a first component which upon heating forms a rigid carbonific char foam having toughness and rigidity, and a second component which upon heating forms an insulative carbonific char foam having a density about half the density of the rigid carbonific foam for insulation properties. The two foam components offer flame retardancy at film thickness of less than 50 millimeters.
Furthermore of interest, U.S. Pat. No. 5,433,991 to Boyd, Jr. et al. discloses a reinforcement system for mastic intumescent fire protection coatings that is a hybrid mesh fabric made from a combination of high temperature and low temperature yarns. The mesh is expandable and stretchable.
Also of interest, U.S. Pat. No. 3,913,290 to Billing et al. discloses a wire mesh and fireproof coating to provide a fire insulation reinforcement for structural members. During fires the coating may lose bonding properties and sections may fall from the member, thus exposing the bare member to the fire. The wire mesh holds the coating in place even though it has lost its bonding effect.
The following U.S. patents are of general background interest. U.S. Pat. No. 5,580,648 to Castle and Gaffney discloses a reinforcement system for mastic intumescent fire protective coatings. Free-floating carbon mesh is embedded in the coatings for reinforcement. U.S. Pat. Nos. 3,913,290 and 4,069,075, both to Billing and Castle, describe the use of mesh to reinforce the char once it forms in a fire. U.S. Pat. No. 5,681,640 to Kiser discloses a passive fire protection system for the protection of conduits, cable trays, support rods, and structural steel against flame and heat in a severe, total-environment type fire. The system includes a multi-layered (laminated), flexible material containing a plurality of layers of intumescent materials, configured to provide containment for the carbonaceous foam resulting from the expansion of the intumescent materials. U.S. Pat. Nos. 4,929,650 and 5,254,190, both to Kurauchi et al., disclose a coating material for tendons for pre-stressed concrete. The material is coated on the tendon surface used in post-tensioning pre-stressed concrete systems in order to protect the tendon from rust and corrosion, and to integrate the tendons with the concrete.
U.S. Pat. No. 4,292,358 to Fryer et al. discloses a heat resistant barrier having one or more layers, each being a support medium in the form of a plurality of closely spaced strands coated with a heat actuated and resistive intumescent coating. The support medium preferably is an expanded metal mesh. U.S. Pat. No. 5,208,077 to Proctor et al. discloses a method for making a composite material of a coated and filled metal strand for use in pre-stressed concrete, stay cables for cable-stayed bridges, and other uses. Internal voids or interstices are filled with epoxy-based resin such that any corrosive media that might penetrate the epoxy coating will be prohibited from migrating through the voids or interstices between and along the cables. U.S. Pat. No. 4,064,359 to Peterson et al. discloses a fire protective insulating product which, when placed about electrical cables, cable trays, or conduits, protects the cable or the like from exposure to open flame temperature of 1600-2000xc2x0 F. (871-1093xc2x0 C.). The inner layer of the protective product is preferably glass fibers in the form of a flexible blanket of approximately one-half to about one inch (1.27 to 2.54 cm) thick. On the glass layer is a fire protective coating, such as a water-based coating. The outer layer also includes a compound that is a source of organically bound halogen to help impart flame retarding. U.S. Pat. No. 4,835,054 to Scarpa discloses a protective covering for electrical cables. The covering has a thermally intumescent coating supported on an open network of metal fibers.
All of the patents and published patent applications mentioned above are incorporated by reference herein.
Despite the prior art as referenced above, there still remains a continuing need to develop protection systems which provide effective thermal protection and corrosion protection to metallic tendons.
Accordingly, the present invention provides a thermally protected and corrosion protected structure particularly suitable for metallic tendons, comprising in combination a core substrate and concentric composite laminate, wherein: (i) the core substrate has a length and extends at least substantially within and is surrounded by the laminate; and (ii) the laminate has a plurality of concentric layers. The concentric layers include: (a) an inner layer of a corrosion protective material substantially along and surrounding the length of the core substrate; (b) a next layer of a first protective plastic coating surrounding the corrosion protective material; (c) a next layer of a heat-resistive intumescent coating surrounding the first protective plastic coating; (d) a reinforcing mesh surrounding and being either on or embedded in the intumescent coating; and (e) an outer later of a second protective plastic coating surrounding the above components.
Consequently, it is an object of the present invention to provide a system that affords both thermal protection and corrosion protection for a core substrate, particularly a substrate that is a tendon for use in post-tensioning systems.